Hi
1/ In standalone mode, ALL pages are AMP. Desktop or mobile. This is what’s now called “Canonical AMP”. For instance, https://ampbyexample.com/ or https://www.ampproject.org/ are “Canonical AMP” websites: all their pages are AMP.
2/ No need for that. All pages are AMP. Having separate versions for AMP and standard HTML is not mandatory at all, it’s just common.
Other question: Do you have theme templates? I found dificult to install your plugin for a magazine website.
We do not have themes, because it’s not a good idea to use a theme. If you have a standard site and you add AMP, then your AMP pages should look similar to your standard website.
So you should customize the AMP pages (with weeblrAMP customizer) to use the same color and styles that your standard website.
Rgds